Saying admit the big 4 can't work implies that line of thinking is fact. It's not. It hasn't worked, and it's definitely challenging, but hasn't yet doesn't equal can't.
Maybe hold your horses and just see what he actually does in a year. People have said for like 2 years running that he wouldn't be able to make the cap work and he has.
Seems to me your view is perhaps to rigid. There are lots of ways to make things work beyond the one or two outcomes you see
It certainly hasn't worked and there is nothing to lead one to believe it will work given the state of the teams other players and prospects. You can always make the cap work by replacing decent players on decent contracts, great contracts even (Kadri) with a bunch of fringe Nhlers at league minimum. The Cap will work but the roster won't as those fringe NHLers can't produce enough come playoff time when the opposition invariably will limit the effectiveness of the big 4 and beat you because their secondary players are way better than yours.
So 40M on 4 guys leaves 40M for the other 16. (going with a bare bones roster of 20 here) that is 2.5M each should be doable? Okay but we need a couple of D-men who are above average. say Muzzin Brodie and Rielly at 7.5M. Oops 18 of our 40M is gone. Need a couple goalies even at this years prices thats another 5M gone. we have added 5 guys so only need 11 now (still 1/2 the team)and we have 17M left. That means 3 D and 8F who average about $1.5M. You might have a chance if you have a few great pieces on ELC's but the prospect pool ain't what it used to be. Maybe trading away picks every year at deadline to go all in hasn't helped on that front either.
In the past he made cap room by moving out bigger salaries and replacing with cheaper. its how he got the cap space to fix the D. moving out guys like Kadri/Johhnson/Kappanen, letting guys like Hyman/Barrie walk. There is no one else to move other than Kerfoot to generate any significant space.
Making the Cap work and building a winning roster within that Cap are two different things. Having 50% of the cap tied up in 4 guys is tough, having all 4 be forwards is worse. Look honestly at this years proposed roster up front. After the big 4, how many would have made Tampa's starting 12 forwards last year. Maybe Kerfoot. Okay Tampa was a bit of a powerhouse and used LTIR rather creatively. How many make Vegas, Mtl or the Islanders? Kerfoot probably does but doubt anymore do.
The playoff opposition will continue to do what Mtl, Columbus and Boston did. Slow down the big four enough so that the top 2 lines are pretty much a wash and beat you with their depth up front.